The Mars South Pole is a prominent region of the Red Planet, marked by a large polar ice cap. This polar region appears as a bright, expansive dome. The South Polar Dome, also known as “The Wart,” is a broad convex feature approximately 500 kilometers in diameter, rising up to 3 kilometers above the surrounding plains. It extends nearly 100 kilometers beyond the permanent ice cap.
Composition and Structure
The Mars South Pole’s composition includes both frozen carbon dioxide (dry ice) and water ice. The permanent ice cap is primarily covered by carbon dioxide ice, a thin layer about 8 meters thick. Beneath this dry ice, and extending beyond it, are extensive polar layered deposits composed mainly of water ice. Radar echoes from the rocky surface beneath these deposits suggest they are at least 90 percent frozen water.
These layered deposits, up to 3.7 kilometers (2.3 miles) deep, record Mars’ climate history. They consist of varying proportions of atmospherically deposited water ice and dust, visible through massive canyons. The layers show variations in color and brightness, highlighting the mix of bright ice and reddish sandy deposits. The total volume of ice in the south polar cap and its adjacent layered deposits is estimated at 1.6 million cubic kilometers.
Unique Features and Discoveries
The Mars South Pole features distinctive geological formations and has been the site of scientific discoveries. One feature is the “araneiform terrain,” or “spiders,” which are branched formations stretching over a half-mile (1 kilometer) with hundreds of spindly “legs.” These features, found in clusters, give the surface a wrinkled appearance and are believed to be carved by processes involving carbon dioxide ice. Experiments simulating Martian conditions have recreated these formations, suggesting that sunlight heating the soil beneath transparent carbon dioxide ice slabs causes the ice to sublimate, building pressure that cracks the ice and releases gas.
A significant discovery involves radar detections of potential subsurface liquid water. In 2018, the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument on the European Space Agency’s Mars Express orbiter identified a “bright spot” approximately 1.5 kilometers (1 mile) below the ice cap in the Planum Australe region. This strong radar reflection was interpreted by some scientists as a 20-kilometer-wide (12.4 miles) lake of liquid water, though further computer simulations suggest compacted ice layers could produce similar echoes. The presence of briny lakes is considered possible due to specific temperature and pressure conditions at the base of the ice cap, potentially aided by natural antifreezes like calcium and magnesium perchlorate.
Climate and Seasonal Dynamics
The Mars South Pole changes throughout the Martian year due to the planet’s orbital mechanics. During the southern Martian winter, the polar region experiences a prolonged period of darkness known as polar night. Temperatures can fall below minus 130 degrees Celsius, causing carbon dioxide to crystallize from the atmosphere and fall as dry ice “snow,” significantly increasing the polar cap’s size. This seasonal snowfall can add 1.5 to 2 meters of dry ice.
As spring arrives in the southern hemisphere, increased solar radiation causes temperatures to rise, leading to the sublimation of carbon dioxide ice. Sublimation is the process where solid ice turns directly into vapor without first becoming liquid, releasing large amounts of gas into the thin Martian atmosphere. This seasonal retreat causes the 600-kilometer-wide ice cover to shrink to a summer diameter of only 400 kilometers. The condensation and sublimation of carbon dioxide, involving about a quarter of the total atmospheric CO2 content, represent a significant Martian climatic cycle, influencing global weather patterns.
Scientific Significance and Future Exploration
The Mars South Pole holds scientific interest, offering insights into the planet’s past climate and astrobiological potential. The layered deposits in the polar cap serve as a geological record, providing data on how water and carbon dioxide have moved across Mars over hundreds of thousands of years. Understanding the history of water on Mars is a central theme in studying whether the planet could have ever supported life, as all known life forms depend on liquid water. The potential confirmation of subsurface liquid water, even if briny, has astrobiological implications, as such environments could harbor microbial life.
The region is also important for future human missions to Mars, as its extensive water ice deposits represent a potential source of resources. Missions like the European Space Agency’s Mars Express, launched in 2003, have studied the south polar region with instruments like MARSIS and the High Resolution Stereo Camera (HRSC), providing detailed maps and insights into its composition and dynamics. Future exploration, potentially involving landers and rovers, aims to further investigate these water reservoirs and their implications for past habitability and sustained human presence on the Red Planet.